Total hip anthroplasty has become a relatively common procedure. It also is becoming more common to replace the prosthesis after a period of time. A difficulty in doing this is that the acetabular shell of the prosthesis will become completely embedded in the surrounding bone and needs to be cut free. The traditional method of accomplishing this has been to use hand-held, curved chisels and a mallet to cut and pry the acetabular shell away from the bone. A problem with this process is that it is difficult to keep the chisel precisely at the periphery of the acetabular shell and often excess bone is removed with the shell.
The X-PLANT acetabular shell removal tool sold by the Zimmer Company reduces this problem to some degree. The X-PLANT removal tool provides a curved chisel having the same contour as the outer periphery of the acetabular shell. The chisel is attached to a shaft having a ball at its extremity which is sized to be inserted into the socket in the polyethylene liner which is located in the acetabular shell to receive the femural head of the prosthesis. As the tool is manipulated and struck with a mallet to break the acetabular shell free from the surrounding bone, the ball pivots in the socket and keeps the chisel blade close to the periphery of the acetabular shell.
While the X-PLANT tool is an improvement over the traditional hand-held chisels, it does have one significant shortcoming. Often the acetabular shell is attached to the pelvis with screws which extend through the shell and into the surrounding bone. These screws need to be removed before the shell can be removed and doing this requires that the polyethylene liner be removed from the shell, which often damages the mechanism which holds the liner in place. As a result the liner moves when the X-PLANT tool is used which prevents the tool from cutting as close to the periphery of the shell as it otherwise would.
The subject invention overcomes the foregoing shortcomings of the prior art tools for removing the acetabular shell by providing a fixture which attaches to the shell. The fixture has a chisel guide mounted on it. The chisel guide causes a chisel to move along a path such that it substantially circumscribes the outer surface of the shell when the chisel is moved.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.